Method for determining the closing point of a pump piston relative to a transverse bore in the pump cylinder

ABSTRACT

A method for determining the closing point of a pump piston relative to a transverse bore in a corresponding pump cylinder, the method including the steps of providing compressed air to the cylinder via the transverse bore, axially sliding the pump piston near the closing point, consecutively measuring two flow values through a throttle cross-section defined by the pump piston and transverse bore, measuring the positions of the piston corresponding to the two flow values and extrapolating the pump piston unto the closing point from the flow values and piston positions.

BACKGROUND OF THE INVENTION

The present invention relates to a method for determining the closingpoint of a pump piston relative to a transverse bore in thecorresponding pump cylinder. In a known method the pressure rise causedby closing the transverse bore with the pump piston is utilized todetermine the end point. Such a method is known from my U.S. patentapplication Ser. No. 542,070 now U.S. Pat. No. 4,546,648. To accomplishthis method a test fluid must be used, thereby resulting in relativelylarge equipment expenses. Another disadvantage of the known method isthat it is only usable for the named purpose.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method whichovercomes the disadvantages of the prior art.

It is a further object to provide a particularly accurate method ofdetermining the closing point of the pump piston relative to thetransverse bore in the pump cylinder.

Additionally, it is an object to provide a method which can alsoquantitatively detect and estimate edge flaws on the piston or thetransverse bore and in addition the piston clearance.

Pursuant to these objects and others which will become apparenthereinafter, one aspect of the invention resides in extrapolating theclosing point by measuring two flow values and their respectivepositions during sliding of the pump piston in the vicinity of theclosing point.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a simplified view of an arrangement for accomplishing themethod of the present invention; and

FIG. 2 is a diagram showing the extrapolation of the closing point.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a pump cylinder 10 having a longitudinal bore 11 inwhich a pump piston 12 is closely slidably guided. The pump piston 12has a front face projecting out of the pump cylinder 10, the front facecontacting a not illustrated cam or eccentric to provide the piston 12with back and forth motion. The upper portion of the longitudinal bore11 forms an exit 13'. A transverse bore 14 penetrates into thelongitudinal bore 11 somewhat under the upper end of the pump cylinder10. A line 15 from an air pressure source 16 is connected to thetransverse bore 14. A pressure control valve 17 is provided in the line15. From the pressure control valve 17 a line 18 leads to a manometer20. A throttle 21 is provided in the line 15 between the pressurecontrol valve 17 and the pump cylinder 10. With the help of the pressureregulator 17 the line 15 is provided with a constant supply pressurep_(e) so that a major pressure ratio exists at a changeable throttlecross-section formed by the transverse bore 14 and an upper or lowerleading edge 22, 22' of the pump piston 12. This pressure ratio for airis p_(e) /p₀ >1.9, wherein p_(e) is a pressure in the line 15 and p_(o)is a pressure downstream of the lower leading edge 22'. The throttle 21serves merely to limit flow when the transverse bore 14 is completelyopened. A line 25 is connected to the exit 13' and leads to a flowmeter26. Alternatively, the flow quantity can be measured indirectly over theworking pressure with help of an orifice 27 which is provided in theline 25' illustrated with a broken line. The pressure drop Δ_(p) and theorifice 27 can be read from a manometer 28. The position of the pumppiston 12 can be read on the front face 12' by a properly positioneddisplacement scale 29.

The determination of the closing point of the pump piston 12, that is tosay the position of the pump piston, which has migrated so that one ofits leading edges 22, 22' just completely closes the transverse bore 14,follows thereby in that through axial sliding of the pump piston 12 inthe vicinity of the closing point, two to be provided flow values Q₂ andQ₁ are consecutively provided and the corresponding positions s₂ and s₁of the pump piston 12 are measured on the displacement scale 29. Withthe help of the pressure regulator 17 a constant inlet pressure p_(e) isfirst provided in the line 15 so that a major pressure ratio exists onthe changeable throttle cross-section defined by the transverse bore 14and the leading edge 22 of the pump piston 12. For air p_(e) /p₀ >1.9 isselected. The flow quantities Q₁ and Q₂ are measured either on the flowmeter 26 or indirectly on the orifice 27.

From the relation derived between the height (h_(i) =s_(i) -s₀) of thecircular segment area of the defined throttle cross-section A_(i) andthe flow quantity, for the purpose of determining a major pressure ratiop_(e) /p₀ on the above-mentioned throttle cross-section

    Q.sub.i =cont·p.sub.e ·A.sub.i ≈const'·p.sub.e ·(s.sub.i -s.sub.0).sup.3/2

Using the determined pairs of values Q₂, s₂ and Q₁, s₁, the closingpoint s₀ can be calculated: ##EQU1##

This approximation formula is sufficiently accurate when the controlarea used for Q₁ and Q₂ is less than or equal to 1% of the entire opentransverse bore 14. By careful selection of the provided values Q₂ andQ₁, namely Q₂ /Q₁ =√8 with for example Q₂ =800 ml/min and Q₁ =283ml/min, the formula is simplified to

    s.sub.o =2 s.sub.1 -s.sub.2.

A further possibility exists in that the piston is moved into theclosing point s₀ ascertained from the described extrapolation method,and any leakage flow Q₀ in this position is determined. Thereby thequality of the leading edge of the front face 22 of the pump piston canbe determined as well as the amount of play between the pump piston andthe pump cylinder.

In the diagram in FIG. 2, the displacement of the pump piston 12 isindicated on the abscissa and the flow values through the throttlecross-section are indicated on the ordinate. At the displacement points₂ the value of Q₂ is measured, and at displacement point s₁ the valueQ₁ is measured. The closing point s₀ is then determined from s₂ and s₁.The leakage flow Q₀ follows from the point s₀.

While the invention has been illustrated and described as embodied in amethod for determining the closing point of a pump piston relative to atransverse bore in a corresponding pump cylinder, it is not intended tobe limited to the details shown, since various modifications andstructural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims:
 1. A method for determining theclosing point of a pump piston relative to a transverse bore in acorresponding pump cylinder, the method comprising the steps of:axiallysliding the pump piston near the closing point; consecutively measuringtwo flow values through a throttle cross-section defined by the pumppiston and the transverse bore; measuring the positions of the pumppiston corresponding to said two flow values; and extrapolating the pumppiston, closing point from said flow values and piston positions; andusing compressed air as a flow medium.
 2. A method as defined in claim1, wherein said measuring steps includes measuring the flow values andpiston positions with a major pressure ratio existing at said throttlecross-section.
 3. A method as defined in claim 1, wherein said flowvalues measuring step includes providing fixed flow values Q₁ and Q₂ inadvance, said position measuring step includes measuring the pistonpositions corresponding to the fixed flow values.
 4. A method as definedin claim 3, wherein said flow values measuring step includes providingfixed flow values with a predetermined relationship.
 5. A method asdefined in claim 4, wherein said flow values measuring step includesproviding fixed flow values having a relationship of Q₂ /Q₁ =√8.
 6. Amethod as defined in claim 4, wherein said flow values measuring stepincludes providing flow value Q₂ as approximately 1% of the maximum flowvalue if the transverse bore were completely open.
 7. A method asdefined in claim 4, wherein said flow values measuring step includesproviding said flow values so that the total difference between thecorresponding piston positions does not exceed roughly 2% of thediameter of the transverse bore, nor have a value under roughly 1% ofthe diameter of the bore.
 8. A method as defined in claim 1, the pumppiston and transverse bore having edges; and further comprising thesteps of moving the pump piston to the closing point and measuring anyflow which may be present in this position for testing the quality ofthe edges of the pump piston and the transverse bore and determiningplay between the pump piston and pump cylinder.